TWICE Special Vinyl ＜THIS IS FOR＞ WORLD TOUR FINALE in SEOUL - LIVE #MINA

In the Korean comments

One top comment reads, in translation, “She’s a princess—a princess,” repeating `"공주다 공주" (gongjuda gongju, she's a princess—a princess)` (gongjuda gongju, “She’s a princess—a princess”) to intensify the compliment rather than identify an actual title.

What the words mean

In `"개이쁘다" (gae-ippeuda, extremely pretty)` (gae-ippeuda, “extremely pretty”), `"개-" (gae, dog; casual intensifier prefix)` (gae-, literally “dog-”) is not about a dog. Here it is a very casual, somewhat coarse intensifier: the commenter is saying Mina is exceptionally pretty.